At present, with the rapid development of network technologies, the demand for a united network, which consists of a cable television network, an Internet Protocol (IP) network and a telecommunication network, becomes more and more urgent. Network providers attach much importance to the service convergence speed when a network fails to function. When a node malfunctions, it is required that switching time for switching a service to a neighbor node is less than 50 ms, and the end-to-end service convergence time is less than 1 s, which have become a threshold of bearer networks.
In order to satisfy the requirement that the service switching time for switching to a neighbor node is less than 50 ms and the end-to-end service convergence time is less than 1 s, such techniques as Multi-Protocol Label Switching Traffic Engineering Fast Re-Routing (MPLS TE FRR) technique and Interior Gateway Protocol (IGP) routing fast convergence technique emerge.
In a double-ascription PE of a Customer Edge (CE) network model, the MPLS TE FRR is usually adopted for service fast switching when the network fails to function. Basic principles of the MPLS TE FRR are: an end-to-end Traffic Engineering (TE) tunnel is established between two PEs, and a backup Label Switching Path (LSP) is established beforehand for a primary LSP which needs protection. Therefore, when a PE detects that the primary LSP is unavailable, such as node malfunctions or link malfunctions, it will switch the traffic to the backup LSP to implement the fast service switching.
With reference to the accompanying FIG. 1, the MPLS TE FRR-based fast service switching under a double-ascription network model will be illustrated in detail hereinafter.
In FIG. 1, PE-E is a double-ascription PE of a remote CE, PE-A and PE-B are both connected to the remote CE, the network model also includes provider's equipment P-C and P-D. A path for an equipment CE-B to visit another equipment CE-A is configured as follows:
CE-B-PE-E-P-C-PE-A-CE-A;
When the node PE-A fails to function, the path for CE-B to visit CE-A is converged to:
CE-B-PE-E-P-D-PE-B-CE-A;
according to standard Multi-Protocol Label Switching Layer 3 Virtual Private Network (MPLS L3 VPN) techniques, firstly, both the PE-A and the PE-B will advertise routes directing to the CE-A to the double-ascription PE-E of the CE-A, and allocate private network labels.
The PE-E selects an optimal Virtual Private Network IPv4 route (VPN V4 route), which is transmitted by a Multi-Protocol Border Gateway Protocol (MP-BGP) neighbor, according to pre-configured strategies. Supposing that the PE-E selects the route advertised by the PE-A as the optimal route, then the PE-E fills in a forwarding item used by a forwarding engine only the routing information advertised by the PE-A, such as a forwarding prefix, an inner layer label, a selected outer layer tunnel, etc. Then the forwarding engine forwards the service according to the routing information.
As to link malfunctions and node malfunctions between the PE-E and the PE-A, wherein, the PE-E and the PE-A are the initial node and the terminal node of the TE tunnel respectively, the MPLS TE FRR can implement the fast service switching.
When the terminal node PE-A of the tunnel fails to function, what is generally adopted is that the CE-A detects the PE-A, which is directly connected with the CE-A, through a bidirectional path detection technique or other techniques. When the CE-A detects there is a malfunction in the PE-A, it will actively switch the traffic to the PE-B to recover the service. But the PE-E can detect the malfunction of the PE-A only through information, such as a Border Gateway Protocol (BGP) neighbor breaks down or an outer layer LSP tunnel is unavailable, etc., and the PE-E re-selects the VPN V4 route advertised by the PE-B. Meanwhile, the PE-E fills in the forwarding item of the forwarding engine with the new routing information, and the forwarding engine forwards the service according to the new routing information, thereby implementing the end-to-end service convergence.
Before the PE-E fills the corresponding forwarding item with the route advertised by the PE-B, the terminal node of the outer layer LSP tunnel directed by the forwarding item of the forwarding engine of the PE-E is the PE-A all the time, and the PE-A has failed to function, therefore during the period from the malfunction appearing in the PE-A to the PE-E filling in the forwarding item with the route advertised by the PE-B, the CE-B is unable to access the CE-A, and the end-to-end service is interrupted.
When the terminal node PE-A fails to function, the time for recovering the normal service transmission mainly depends on the service convergence time which is closely related to the number of the MPLS VPN inner routes and the number of hops of a bearer network. Typically, the service convergence time is about 5 s, which is far from the requirement that the end-to-end service convergence time should be less than 1 s, moreover, the end-to-end service convergence time will increase significantly with the increase in the number of the MPLS VPN private network routes.